cloudbuild: upgrade to E2_HIGHCPU_32 to fix session timeout

Multi-arch builds (linux/amd64 + linux/arm64) take ~12 min on N1_HIGHCPU_8,
causing the BuildKit session to expire before the push phase completes:

  error: no active session: context deadline exceeded

Other K8s repos with large multi-arch binaries (aws-ebs-csi-driver,
cloud-provider-gcp) use E2_HIGHCPU_32 which completes builds in ~3-5 min,
well within the session window.

Author: Ganiredi

cloudbuild.yaml

@@ -2,7 +2,7 @@
 options:
   dynamic_substitutions: true
   substitution_option: ALLOW_LOOSE
-  machineType: 'N1_HIGHCPU_8'
+  machineType: 'E2_HIGHCPU_32'
 steps:
   - name: gcr.io/cloud-builders/git
     args: ['fetch', '--tags']